Various fixes and changes based on tester feedback

module/applications/sheets/class-sheet.mjs

@@ -28,15 +28,26 @@ export default class OathHammerClassSheet extends OathHammerItemSheet {
     return context
   }
 
-  /** @override — collect checkbox sets explicitly so unchecking all works */
-  _prepareSubmitData(event, form, formData) {
-    const data = super._prepareSubmitData(event, form, formData)
-    data["system.armorProficiency"] = Array.from(
-      form.querySelectorAll('input[name="system.armorProficiency"]:checked')
-    ).map(el => el.value)
-    data["system.weaponProficiency"] = Array.from(
-      form.querySelectorAll('input[name="system.weaponProficiency"]:checked')
-    ).map(el => el.value)
-    return data
+  /** @override */
+  _onRender(context, options) {
+    super._onRender(context, options)
+    // Handle proficiency checkboxes directly — FormDataExtended mishandles
+    // multiple same-named checkboxes, so we intercept the change event,
+    // collect all checked values ourselves, and stop propagation to prevent
+    // the generic submitOnChange handler from clobbering the data.
+    for (const cb of this.element.querySelectorAll('.proficiency-checkboxes input[type="checkbox"]')) {
+      cb.addEventListener("change", this.#onProficiencyChange.bind(this))
+    }
+  }
+
+  async #onProficiencyChange(event) {
+    event.stopPropagation()
+    const root = this.element
+    const armorProficiency  = [...root.querySelectorAll('input[name="system.armorProficiency"]:checked')].map(e => e.value)
+    const weaponProficiency = [...root.querySelectorAll('input[name="system.weaponProficiency"]:checked')].map(e => e.value)
+    await this.document.update({
+      "system.armorProficiency":  armorProficiency,
+      "system.weaponProficiency": weaponProficiency,
+    })
   }
 }